In a prior art system in the field of this invention, it is known to use a hardware element in the form of a SAW (Surface Acoustic Wave) ceramic filter at the output of the power amplifier of a DCS transmitter to remove the noise generated in the WCDMA Receiver. This external filter is called notch filter since it is notching the generated TX (transmit) noise of the DCS in the WCDMA RX (receive) band. Since the WCDMA RX band is at minimum at 2110 Mhz and the DCS TX upper frequency is at 1980 Mhz, the delta in frequency is small, i.e., 130 Mhz, and since the power amplifier noise can be as high as 40 dB greater than the required level of receive noise, this results in the need to have a notch filter that filters more than 40 dB in a 130 Mhz offset at 1980 Mhz frequency, requiring a high Q filter, thus resulting in a higher insertion loss in the range of 1.5 dB-1.8 dB, which requires the output power in the DCS or PCS transmitter to be increased, which reduces the mobile's talk time significantly (e.g., by 20%).
Additionally, this known approach has the disadvantages that:                providing an external notch filter in order to allow simultaneous monitoring of WCDMA RX during a DCS or PCS TX requires an extra part to be added, resulting in extra cost (typically in the range of US$1 for the SAW filter and matching element)        extra PCB space (typically of the order of 70 mm2) must be provided for the extra part(s)        lower output power is available at the antenna in DCS or PCS band, due to the extra insertion loss of the notch filter, resulting in a potential issue to comply with the 3GPP (3rd Generation Partnership Project) specification.        The external notch filter attenuation also changes over temperature, resulting in difficulty to achieve desired attenuation (e.g., 40 dB) in the WBCDMA RX band over the temperature range of a mobile cellular unit.        
The above disadvantages are increased if the mobile is required to support 2 types of dual mode operation, as in a 3G ‘world phone’, where at the same mobile unit UMTS is supported in Europe (WCDMA in 2110 Mhz and DCS) and WCDMA and PCS are supported in the US bands, resulting in two notches and more stringent notch insertion loss for the US case since the PCS band will be near the WCDMA band in the PCS band.
A need therefore exists for FDD monitoring during TDD call wherein the abovementioned disadvantage(s) may be alleviated.